The proposed project seeks to establish a quantified, reliable, and repeatable measurement technique in a rabbit model for the assessment of the functional condition of corneal innervation. The methods to be used will be a combination of techniques gleaned from the field of animal learning and of procedures developed in animal somatosensory psychophysics. In the first part of the project, the absolute thresholds of corneal sensitivity to tactile stimulations will be obtained from rabbits responding reflexively in a conditioned avoidance paradigm. In successfully trained animals, a previously shock-conditioned leg push reflex will indicate sensory awareness of the stimulation of the cornea by an electromagnetically actuated esthesiometer. In the second series of experiments, electromyographic and cardiac response measurements to increasing stimulation intensity steps will be combined in classical psychophysical and signal detection theory sensitivity measurement procedures. The calculated data will provide the basis for the graphical representation of normal corneal stimulus response functions in the rabbit. Deviations from such standardized graphical functions can be interpreted to be reflections of abnormal sensory processing; therefore they will be held to represent changes in corneal innervation and, indirectly, of the condition of the cornea. This functional rabbit model should be sensitive to relatively subtle changes in the condition of corneal innervation; therefore such a model should provide a reasonable substitute for current methods which assess toxicity of substances applied to the eye by frequently producing serious injury to the ocular surface and suffering in the experimental animal. Since the stimulations are non-invasive and the subjects are not required to respond verbally, similar objective techniques should be useful in clinical work.